// Problem: 
// Contest: 
// URL: 
// Memory Limit: 
// Time Limit: 
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#include<bits/stdc++.h>
using namespace std;
#define int long long
inline int read(){
	int s=0,w=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
	return s*w;
}
int a,b,c;
bool f(double x)
{
	double d=a;
	for(int i=1;i<=c;i++)
	{
		d=d*(1+x)-b;
	}
	return d>=0;
}
signed main()
{
	cin>>a>>b>>c;
	double l=0.0,r=3.0;
	while(r-l>=0.0001)
	{
		double mid=(r-l)/2+l;
		if(f(mid))r=mid;
		else l=mid;
	}
	printf("%0.1lf",l*100);
	return 0;
}
